Automobile traction control systems function to prevent the vehicle tires from rotating without gripping the road due to excessive drive force when the vehicle is traveling or accelerating on a slippery road surface, such as a road covered with ice, snow or gravel. This may be achieved by cutting fuel supply to the engine so as to decrease the drive force.
A fuel cut controller for this purpose is described for example in Tokkai Hei 4-295146 published in 1992 and 1-227830 published in 1991 by the Japanese Patent Office.
In this controller, the rotation speeds of the drive wheels and driven wheels are detected, and a slip factor between the drive wheels and road surface is computed from the difference between the two speeds. When the slip factor is greater than a set value, the fuel supply to a predetermined cylinder of the engine is cut based on the slip factor. As a result, when the vehicle starts to slip due to excessive drive force, the drive force of the drive wheels is rapidly decreased so as to suppress the slip.
However, when the fuel supply to some of the engine cylinders is cut, the air supplied to cylinders to which fuel supply has stopped, and exhaust including unburned fuel from cylinders to which fuel supply has not stopped, flow into the catalytic converter in the exhaust system. Depending on the engine running conditions, unburned fuel in the converter may react with the air, thereby causing the catalyst temperature to rise above the tolerance level and leading to catalyst deterioration.
In the aforesaid controller, the period during which fuel cut is performed is limited, and fuel cut is prohibited for a certain period after a preceding fuel cut has been made, so that the catalyst temperature does not rise above a certain level.
According to this controller, however, fuel cut is subsequently prohibited for a predetermined period when fuel cut has continued for a prescribed time, and fuel supply is then restarted to all cylinders even when the slip factor of the drive wheels is large. Hence, although temperature rise of the catalytic converter is prevented, the engine drive force cannot be adequately suppressed, and the effect of preventing the drive wheels from slipping remains limited.